The present invention relates to a device for assembling two parts exhibiting lateral positional play in a given direction.
The invention will find a particularly advantageous application especially, but not exclusively, in the field of motor-vehicle construction.
In industry in general, it is often necessary, by means of fixing screws, to have to assemble parts which exhibit positional play between them. This play may be lateral play in a direction X, in the sense that the parts are not contiguous, and are separated by a certain gap in the X direction. The positional play may also be transverse, in the YZ plane perpendicular to X, which is manifested by the fact that the parts are not exactly opposite one another, the fixing holes for the parts to be assembled no longer being in coincidence.
This type of situation is encountered in particular in motor-vehicle construction, when it is a question of assembling the internal front crosspiece which carries a certain number of accessories (the dashboard, air-conditioner, airbag, etc), to the pillars lying on either side of the passenger compartment of the vehicle. With the tolerances in this field being wide, the said crosspiece most often exhibits relatively substantial positional play with each of the pillars.
In order to remedy this drawback, it is possible to take up the transverse positional play in the YZ plane by using fixing holes which are not circular but oblong. As far as the lateral positional play in X is concerned, there exist means for compensating for the gap between the two parts, such as the insertion of washers, or of an adjustable spacer consisting of five different elements as is described in the U.S. Pat. No. 4,682,906, for example.
However, none of these known means is really satisfactory, since they are awkward to put into practice, in the case of the system with washers, or very complex, in the case of the adjustable spacer.
Hence, the technical problem to be resolved by the object of the present invention is to propose a device for assembling the two parts featuring lateral positional play in a given direction, which is simple both in its use as well as in its composition.
The solution to the technical problem posed consists, according to the present invention, in that the device includes, all aligned in the said given direction:
a smooth through-hole formed in a first part,
a fixing screw able to be moved freely through the said smooth through-hole and carrying a threading of a first type,
a tapped through-hole of a second type, formed directly or indirectly on the second part opposite the smooth through-hole,
a spacer carrying, on the one hand, an external threading of the said second type, able to interact with the said tapped through-hole, and, on the other hand, an internal tapping of the said first type, able to interact with the said fixing screw, the coefficient of friction provided, directly or indirectly, between the fixing screw and the spacer being different from the coefficient of friction provided, directly or indirectly, between the spacer and the tapped through-hole.
The characteristics of the friction coefficient are, for example, related to the angle of the thread of the threadings/tappings and/or to the properties of the materials present, especially of those of the friction members possibly provided between the said fixing screw, the said spacer and/or the said tapped through-hole.
In what follows, xe2x80x9ctypexe2x80x9d of threading or of tapping will be understood to be either xe2x80x9cright-handxe2x80x9d or xe2x80x9cleft-handxe2x80x9d. For example, if the said first type of threading of the fixing screw and of internal tapping of the spacer is designed to be right-hand, then the second type of tapping of the tapped through-hole and of external threading of the spacer will be designed to be left-hand.
Thus, as will be seen in detail later, the assembly device in accordance with the invention functions in the following manner, for a coefficient of friction between the fixing screw and the spacer higher than the coefficient of friction between the spacer and the tapped through-hole.
The fixing screw is first of all engaged in the spacer, fixed to the second part, through the smooth through-hole of the first part. It is then actuated and penetrates into the spacer until the friction between the fixing screw and the spacer becomes sufficiently high for the drive movement applied to the screw to cause the rotation of the spacer in the tapped through-hole, the fixing screw and the spacer remaining fixed with respect to one another.
Because of the tapping and of the inverse threading, the screw/spacer assembly then moves in a translational movement inverse to the direction of insertion of the screw into the spacer. In the course of this movement, the spacer becomes engaged in the gap between the two parts to be assembled, until it comes into abutment against the first part. At that moment, the fixing screw can again penetrate into the spacer, until it comes to bear against the first part. The two parts are then completely and positively assembled.
It will be noted that employing the assembly device of the invention is very simple, since the only action which it requires is the rotational movement of the fixing screw. Moreover, only two elements are necessary to produce it, namely a tapping applied to the second part, and a spacer interacting with the said tapping and the fixing screw.